LT4256-3IGN Linear Technology, LT4256-3IGN Datasheet

Page 1

... An external resistor string from V overvoltage protection. The LT4256-3 is available in a 16-lead SSOP package. , LTC and LT are registered trademarks of Linear Technology Corporation. Hot Swap is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. ...

Page 2

... V ≤ 80V CC V – 48V GATE OUT OUT U W TOP VIEW ORDER PART V 16 NUMBER CC SENSE 15 LT4256-3CGN NC 14 LT4256-3IGN GATE OUT PART MARKING FB 10 TIMER 9 42563 GN PACKAGE 42563I = 125°C, θ = 130°C/W JA http://www.linear.com/leadfree/ MIN TYP MAX ● ...

Page 3

... Driving this pin to a voltage beyond the clamp voltage may damage CC the part 3.5 3.0 2.5 2.0 1.5 1.0 0 (V) CC 42563 G02 LT4256-3 MIN TYP MAX UNITS ● 3.95 3.99 4.03 V ● 4.20 4.45 4.65 V 0.3 0.45 0.60 V 0.25 0.4 V 0.60 1.0 V µA 0.1 1 µ ...

Page 4

... LT4256 TYPICAL PERFOR A CE CHARACTERISTICS Specifications are 25°C unless otherwise noted. A GATE Pull-Up Current vs Temperature 0 –5 –10 –15 –20 –25 32µA @ 25°C –30 –35 –40 – 100 –25 TEMPERATURE (°C) 42563 G04 V – V Voltage GATE OUT vs Temperature 18V 12V 10. –50 –25 ...

Page 5

... TEMPERATURE (°C) 0.2 L-H THRESHOLD 0.1 0 –0.1 –0.2 –0.3 –0 100 42563 G16 LT4256-3 OV Thresholds vs Temperature 4.1 L-H THRESHOLD 4.0 3.9 3.8 3.7 H-L THRESHOLD 3.6 3.5 20 –50 – TEMPERATURE (°C) 42563 G19 PWRGD Output Voltage vs I PWRGD ...

Page 6

... If RETRY is floating or connected to a voltage above its 1.2V threshold, the LT4256-3 automatically restarts after a current fault. Under an output short-circuit condition, the LT4256-3 cycles on and off with a 3% on-time duty cycle. FB (Pin 10): Power Good Comparator Input. FB monitors the output voltage through an external resistive divider. ...

Page 7

... To defeat current limit, connect SENSE (Pin 16): Input Supply Voltage. The positive supply CC input ranges from 10.8V to 80V for normal operation typically 1.8mA. An internal circuit disables the LT4256-3 for inputs less than 9.8V (typ). LT4256-3 . When OUT by 2V, the 62mA is reduced to 130µA ...

Page 8

... LT4256-3 W BLOCK DIAGRA GEN REF GEN 3.99V 7V 100k 7 RETRY – INTERNAL + 9.8V + 0.65V TIMER LOW – + TIMER HIGH – 4.65V 8 SENSE 15 + OPEN 3mV CIRCUIT – – CURRENT 14mV TO 55mV LIMIT + + FOLDBACK – UV – 4V LOGIC UV + – OPEN 12 V OUT CHARGE PUMP AND ...

Page 9

... UV t PLHUV GATE V +2V OUT Figure GATE Timing 4.45V FB t PLHFB 1V Figure PWRGD Timing OUT – SENSE 55mV t PHLSENSE V CC GATE Figure 4. SENSE to GATE Timing LT4256-3 + – 100pF 3.6V t PHLUV V +2V OUT 4256 F02 3.99V t PHLFB 1V 4256 F03 4256 F04 42563fa 9 ...

Page 10

... The transient currents can permanently damage the con- nector pins and glitch the system supply, causing other boards in the system to reset. The LT4256-3 is designed to turn on a board’s supply voltage in a controlled manner, allowing the board to be safely inserted or removed from a live backplane. The ...

Page 11

... OFF SIGNAL Q2 FROM MPU VN2222 0.01µF GND Figure 7. How to Use a Logic Signal to Control the LT4256-3 Turn On/Off W U noise spikes and capacitively coupled glitches from shut- ting down the LT4256-3 output erroneously. To calculate UV and OV thresholds, use the following equations: ...

Page 12

... FB. If the LT4256-3 goes into current limit when the voltage 0V, the current limit circuit drives GATE to force a constant 14mV drop across the sense resistor. As the ...

Page 13

... Latch Off Operation If RETRY is grounded, the LT4256-3 will latch off after a current fault. After the part latches off, it may be com- manded to start back up. This is accomplished by cycling UV to ground and then back high (this command can only be accepted after TIMER discharges below the 0 ...

Page 14

... OPEN to be externally pulled high. OPEN is always active when V (the internal UVLO threshold), OPEN is pulled low. Open-circuit MOSFETs are detected with the LT4256-3 by monitoring the voltage across R5 with OPEN while moni- toring the output voltage with PWRGD. An open FET condition is signalled when OPEN is high and PWRGD is low (after the part has completed its start-up cycle) ...

Page 15

... PULL-DOWN Figure 13. Delay Circuit for OPEN FET Detection W U Supply Transient Protection The LT4256-3 is 100% tested and guaranteed to be safe from damage with supply voltages up to 80V. However, , given STARTUP voltage transients above 100V may cause permanent damage. During a short-circuit condition, the large change ...

Page 16

... In some applications it may be possible for V below ground (due to the parasitic trace inductance). Higher current applications, especially where the output load is physically far away from the LT4256-3 will be more susceptible to these transients. This is normal and the LT4256-3 has been designed to allow for some ringing below ground ...

Page 17

... U U APPLICATIO S I FOR ATIO In order to use this feature as designed, a bidirectional Zener diode is needed for D1. When the LT4256-3 com- mands the MOSFET off (and a bidirectional Zener is used), the output discharges very slowly (t 130µA). Several variations can be implemented to dis- charge the output faster. The recommeded method is shown in Figure 17 and uses an external PNP transistor, diode and resistor to discharge the output quickly ...

Page 18

... V traces. The minimum trace width for 1oz copper foil is 0.02" per amp to make sure the trace stays at a reasonable temperature. 0.03" per amp or wider is recommended. Figure 18 shows a layout that meets these requirements LT4256 Figure 18. Recommended Component Placement ...

Page 19

... TYP .008 – .012 (0.203 – 0.305) TYP LT4256-3 .189 – .196* (4.801 – 4.978) .009 (0.229 REF .150 – .157** (3.810 – 3.988) ...

Page 20

... Hot Swap Controller in SOT-23 LTC4252-1/LTC4252-2 – 48V Hot Swap Controller in MSOP LTC4253 – 48V Hot Swap Controller and Supply Sequencer LT4254 Positive High Voltage Hot Swap Controller LT4256-1/LT4256-2 Positive High Voltage Hot Swap Controller Linear Technology Corporation 20 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● ...